I've run approx 2K rounds of the poly coated Wolf through my 53 with no ill effects other than an exceptionally dirty gun.

Here's what HK had to say about steel cased ammunition:

"Cartridge case obturation, the greatest uncertainty factor in every automatic weapon, is reduced so much by the introduction and further development of the fluted chamber and has become uniform for all types of cartridge cases, including lacquered steel cases, that operation is reliable in every situation, even under the most adverse firing conditions. - Heckler & Koch, GmbH 1970"